firewire: core: make transaction label allocation more robust

If one request is so long-lived that it does not get a response before
the following 63 requests, its bit in tlabel_mask is still set when the
next request tries to allocate a transaction label for that number.  In
this state, while the first request is not completed or timed out, no
new requests can be submitted.

To fix this, skip over any label still in use, and do not error out
unless we have entirely run out of labels.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/core-transaction.c

@@ -229,6 +229,23 @@ static void fw_fill_request(struct fw_packet *packet, int tcode, int tlabel,
 	packet->payload_mapped = false;
 }
 
+static int allocate_tlabel(struct fw_card *card)
+{
+	int tlabel;
+
+	tlabel = card->current_tlabel;
+	while (card->tlabel_mask & (1ULL << tlabel)) {
+		tlabel = (tlabel + 1) & 0x3f;
+		if (tlabel == card->current_tlabel)
+			return -EBUSY;
+	}
+
+	card->current_tlabel = (tlabel + 1) & 0x3f;
+	card->tlabel_mask |= 1ULL << tlabel;
+
+	return tlabel;
+}
+
 /**
  * This function provides low-level access to the IEEE1394 transaction
  * logic.  Most C programs would use either fw_read(), fw_write() or
@@ -290,16 +307,13 @@ void fw_send_request(struct fw_card *card, struct fw_transaction *t, int tcode,
 
 	spin_lock_irqsave(&card->lock, flags);
 
-	tlabel = card->current_tlabel;
-	if (card->tlabel_mask & (1ULL << tlabel)) {
+	tlabel = allocate_tlabel(card);
+	if (tlabel < 0) {
 		spin_unlock_irqrestore(&card->lock, flags);
 		callback(card, RCODE_SEND_ERROR, NULL, 0, callback_data);
 		return;
 	}
 
-	card->current_tlabel = (card->current_tlabel + 1) & 0x3f;
-	card->tlabel_mask |= (1ULL << tlabel);
-
 	t->node_id = destination_id;
 	t->tlabel = tlabel;
 	t->callback = callback;